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Vicarious fear induction and avowed autonomic stereotypy
Behav. Res. & Therapy, 1972, Vol. 10, pp. lOSto 110. Pergamon Press. Printed in England
VICARIOUS FEAR INDUCTION AND AVOWED AUTONOMIC STEREOTYPY ROBERT
1.
EDELMAN
Florida Technological University, Orlando, Fla. 32816, U.S.A. (Received 19 August 1971)
Summary-Peripheral psychophysiological arousal was observed in subjects instructed to imaginepreviously determined fear vs. neutral situations. Critical features of the experimental design were: 1. The preselection of subjects on the basis of avowed autonomic stereotypy, 2. Minimizing experimenter bias effects and 3. Running separate groups of male and female subjects. Results indicated that fear scenes produced greater arousal than neutral scenes but only in that channel of maximal autonomic lability for a given subject. DESENSIllZATION theory
has relied heavily upon the autonomic nervous system as a mediator of anxiety. However, these mediating processes have typically been inferred from behavioral criteria and it is only quite recently that direct measures of physiological arousal have been obtained. Evidence is already extant to indicate that in vivo presentation of fear-invoking stimuli does in fact result in peripheral psychophysiological arousal (Edelman, 1970; Hodges and Spielberger, 1966). The evidence is less clear cut however, concerning the activating potential of vicarious stimulus presentation. Essentially representative of centralist position, this proposition maintains that peripheral autonomic arousal occurs as a consequence of a central process induced by the instructional set of imagining a fearful situation. Evidence supporti ve of this proposition was provided by Grossberg and Wilson (1968) who found skin conductions (SC) and heart rate (RR) to be elevated in female subjects told to imagine fear invoking situations . An interpretive difficulty was found in that study however in that control subjects, neutral to the content of the scenes, were not physiologically differentiated by the reading of the scene relative to subjects avowing fear to that scene except on the HR measure. A follow-up on the Grossberg and Wilson study (Edelman, 1971) using male subjects did not lend support to the activating potential of vicarious stimulus presentation on physiological processes. That study found that the reading of predetermined fear invoking scenes reliably accelerated heart rate but that when subjects were under the instructional set to imagine the scene, heart rate was at best marginally differentiated from basal level. It is also noteworthy that in both of these aforementioned studies, muscular tension (EMG) typically decreased during the presentation of the vicarious fear stimuli. This latter fact is of importance in that some early theorists had proposed peripheral control of autonomic tension through the skeletal musculature (Jacobson, 1938). The purpose of the present study was to replicate aspects of previous studies relating central arousal and peripheral autonomic processes and to add several procedures which previous research has suggested should be of importance. First of all, subjects were chosen for experimental participation on the basis of their avowed channel of maximal autonomic response. Several investigators have noted stereotypy in autonomic response such that 105
106
ROBERT I. EDELMAN
subjects respond consistently in a particular autonomic end-organ across stressors (Lacey et al., 1951; Lacey and Lacey, 1958). Subjects in the present study were chosen. on the basis of being either heart-rate responders and not GSR responders or GSR responders and not heart-rate responders on the basis of Stern's (1969) Perceived Somatic Reactions to Stress questionnaire. Since there are insufficient validity data relevant to this scale to indicate irs efficiency in predicting autonomic stereotopy, positive results in the present study would tend both to establish the validity of the major proposition at hand while at the same time providing validation data for Stern's scale. A second feature of this experiment was that separate groups of male and female subjects were exposed to the vicarious stimulus presentation. It will be recalled that the Grossberg and Wilson study using female subjects essentially supported the major proposition at hand while the Edelman study using male subjects did not. A final feature of this investigation was that procedural precautions were taken to minimize possible experimenter bias in the presentation of the fear and neutral scenes. This was accomplished by having one experimenter determine the fear and neutral scenes, while a second experimenter simply read the scenes to S in a separate criterion session. The second E was not informed as to which scene was neutral and which was fear-inducing for a given subject. The major hypotheses of the present study may be stated as follows: (1) Subject's verbal report to Stern's scale would reliably predict their channel of maximal autonomic response. (2) The vicarious presentation of arousing material would result in peripheral psychophysiological arousal but only in that channel of maximal autonomic response. (3) Muscular tension would not co-vary with autonomic processes and, since subjects were preselected on the basis of autonomic response and not EMG response, vicarious stimulation would not result in increased muscular tension. (4) Statistically reliable results would be found for female subjects but not for male subjects. METHOD Subjects The subjects were 16 male and eight female students from an introductory psychology class who received extra credit for participation. Ss were chosen from a pool of 187students on the basis of their responses to a modified version of Stern's (1969) Perceived Reactions to Stress questionnaire. In its original form, this questionnaire asks Ss to indicate which of II physiological responses constitute their reaction to personally stressful situations. In the present study, Ss were asked to rank order their response to stress along an intensity dimension and also a frequency dimension using Stern's 11 categories. The purpose of using two separate rank-orderings was to increase the discriminitive power of the instrument and also to avoid the inclusion of Ss who might have responded carelessly or randomly to the group-administered questionnaire. The questionnaire was administered approximately two weeks prior to the actual experimental run. Eight of the 16 male Ss were avowedly high GSR (HGSR) responders but low heart rate (LHR) responders, scoring 0.98 standard deviations (SDs) above the class mean for GSR and 1.03 SDs below the mean for HR reactivity. The remaining eight male Ss avowed the opposite patterning of autonomic responding (LGSR-HHR), scoring 0.90 sn s above the mean for HR and 0.68 sn s below the mean for GSR. The same selection procedure prevailed for females. However, it was not found possible to recruit a sufficient number of Ss for the LGSR-HHR condition who met the
VICARIOUS FEAR INDUCTION AND AVOWED AUTONOMIC STEREOTYPY
107
dual criteria of avowed differential autonomic patterning and willingness to participate in the experiment and this group was accordingly dropped. Scores on the reaction to stress questionnaire for the HGSR-LHR Ss were 0.58 SDs above and 0.85 SDs below the class mean for GSR and HR respectively. Apparatus All physiological variables were monitored on an E & M physiograph. Heart rate was recorded from plate electrodes placed over the wrists and coated with Redux conductive jelly. GSR was recorded using AgjAgCI electrodes coated with redux and placed on the Palmar surface of the second and fourth fingers of the left hand. EMG was recorded from the frontalis muscle according to Lippold's recommendations using AgjAgCI stick-on electrodes coated with Redux. Experimental design and procedure The experimental run for a given subject rook place in two sessions spaced, on the average, a week apart. In the first session, the experimenter explained in detail the purpose of the experiment and what it would entail from the subjects viewpoint. The Fear Survey Schedule (Wolpe and Lang, 1969)was then administered to serve as a vehiclefor determining S's salient fears. After completing the survey, Ss were asked about other fears they might have which were not covered by the survey. The Es were programmed to behave in a friendly manner to encourage self-disclosure, and this first session usually lasted close to an hour. After there was agreement as to S's most important fear both E and S collaborated in writing a 50 word description of that scene devoid of emotionally charged words. The neutral scene was constructed similarly utilizing an item from the survey to which S indicated no anxiety, thereby terminating this first session. A different same-sexed E ran the Ss in the second session. This E was provided with the previously obtained scenes but had no information as to which was the fear and which the neutral scene. S was seated in an overstuffed chair and the appropriate recording electrodes attached. Each scene was then read twice following a counterbalanced ABBA design. The reading of each scene itself consisted of three separate conditions; a 30 sec base period, a 30 sec period at which time the scene was read and finally, a 30 sec period at which time S was given the instructional set to imagine the scene. Each scene presentation was separated by a two minute period to allow physiological measures to stabilize. The experimental design then, was a 2 x 2 x 3 with repeated measures on the last two factors representing respectively the variables Autonomic Stereotypy (HGSR-LHR, LGSR-HHR), Scene Type (fear vs. neutral) and Vicarious Stimulus Presentation (base vs. reading VS. imagining). RESULTS Quantification The quantification procedure followed rules described in a previous study (Edelman, 1971). Data reduction was carried out by a technician unfamiliar with the details or purpose of the study. GSR was converted to micromhos and EMG was converted to millivolts prior to the statistical analyses. Male subjects The GSR and HR data were analyzed according to a type 2 repeated measure & analysis of variance (Winer, 1962, p. 319(. For HR, statistically reliable results were obtained for Scene Type (F-17.30, 4f-l/14, p
108
ROBERT I. EDELMAN
df=2f28, p
/
80
• 78
-----.
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a. .a
76
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r
74
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72 -
70
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....-
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...-- / ./
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Imogine
Cond ition
Fro . 1. Heart rate for male subjects as a function of condition, avowed autonomic response and type of trial.
A similar statistical analysis performed on the GSR data did not attain significance. The EMG data were analyzed by a 2 x 3 repeated measures ANOVA and were not statistically reliable.
Female subjects The EMG, GSR and HR data were analyzed using 2 x 3 repeated measures AN OVA's representing the variables Scene Type and Vicarious Presentation. Statistically reliable results were obtained for Vicarious Presentation (F=4.0, df=2fI4, p<0.05) on the skin conductance measure. Moreover, multiple range tests indicated that skin conductance was reliably higher (p<0.05) during the imagining of the fear scene compared with the neutral scene as can be seen in Fig. 2. DISCUSSION Probably the most salient finding of the present investigation was that imagining a fearful situation elevated autonomic processes more than did a neutral situation. These findings appear consistent with Wolpe's (1969) contention that autonomic processes can
VICARIOUS FEAR INDUCTION AND AVOWED AUTONOMIC STEREOTYPY
109
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3·80
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.... 0
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. - - . Neutral trial
•
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Imagine
Condition
FIG.2. Skin conductance for female subjects avowing high reactivity as a function of condition.
be altered by central states . An important qualification to this statement in the present study, however, is that such arousal is likely to occur in that autonomic channel which is most labiel for a given subject. This finding serves in part to highlight the fact that there is not isomorphic correspondence between autonomic and behavioral measures of anxiety. Under any given set of experimental conditions, these two measures may be correlated or completely uncorrelated-a state of affairs which has led to numerous research strateg ies to enhance the degree of concordance between these measures. Thus, some investigators (Houston, 1971; Thayer, 1971) have attempted to attenuate presumed distorting factors in self-reports, while others (Paul, 1969) including the present investigator have attempted to refine autonomic methodology to achieve greater concordance with behavioral measures. Thus, while the present study does lend credence to Wolpe's position, it is suggested that considerable caution be exercised concerning the general question of defining anxiety as an autonomic response. It is also noteworthy that Stern's scale appeared to have predictive value concerning autonomic arousal. While this finding was not invariant in the present study, it does appear to have heuristic value for autonomic nervous system research which is generally characterized by extremely high inter-subject variability. In the present study, autonomic arousal and muscular tension appeared to occur quite independentl y. This finding is quite consonant with prior research which has generally been inconsistent with the notion that autonomic arousal must be peripherally controlled. REFERENCES R. I. (1971) Desensitization and physiological arousal. J. Person. soc. Psychol. 17, 259-266. R. I. (1970) Verbal report as a prognosticator of physiological arousal to threat. J. abnorm. Psychol. 76, 492-495.
EDELMAN EDELMAN
110
ROBERT I. EDELMAN
HODGES W. F. and SPIELBERGER C. D. (1966) The effects of threat of shock on heart rate for subjects who differ in manifest anxiety and fear of shock. Psychophysiol. 2, 287-294. HOUSTON B. K. (1971) Trait and situational denial and performanceunder stress. J. Person. soc. Psychol. 18, 289-293.
JACOBSON E. (1939) Variation of blood pressure with skeletal tension and relaxation. Ann. Int. Med. 12, 1194-1212.
LACEY J. I. and LACEY BEATRICE C. (1958) Verification and extensionof the principleof autonomic response stereotypy. Am. J. Psychol. 71, 50-73. LACEY J. I. and VAN LEHN R. (1952) Differentialemphasis in somatic response to stress. Psychosom. Med. 23, 185-193.
PAUL G. L. (1969) Physiological effects of relaxation training and hypnotic suggestion. J. abnorm. Psycho/. 74, 425-437.
STERN R. M. and HIGGINS J. D. (1969) Perceived somatic reactions to stress: sex, age and familial occurrence. J. Psychosom. Res. 13, 77-82. THAYER R. E. (1971) Personality and discrepencies between verbal reports and physiological measures of private emotional experiences. J. Personality. 39, 57-69. WINER B. J. (1962) Statistical Principles in Experimental Design. McGraw-Hill, New York. WOLPE J. and LANG P. J. (1969) Fear Survey Schedule Manual. Ed. & Industrial Testing Service. WOLPE J. and LAZARUS A. A. (1966) Behavior Therapy Techniques. Pergamon Press, Oxford.
VICARIOUS FEAR INDUCTION AND AVOWED AUTONOMIC STEREOTYPY ROBERT
1.
EDELMAN
Florida Technological University, Orlando, Fla. 32816, U.S.A. (Received 19 August 1971)
Summary-Peripheral psychophysiological arousal was observed in subjects instructed to imaginepreviously determined fear vs. neutral situations. Critical features of the experimental design were: 1. The preselection of subjects on the basis of avowed autonomic stereotypy, 2. Minimizing experimenter bias effects and 3. Running separate groups of male and female subjects. Results indicated that fear scenes produced greater arousal than neutral scenes but only in that channel of maximal autonomic lability for a given subject. DESENSIllZATION theory
has relied heavily upon the autonomic nervous system as a mediator of anxiety. However, these mediating processes have typically been inferred from behavioral criteria and it is only quite recently that direct measures of physiological arousal have been obtained. Evidence is already extant to indicate that in vivo presentation of fear-invoking stimuli does in fact result in peripheral psychophysiological arousal (Edelman, 1970; Hodges and Spielberger, 1966). The evidence is less clear cut however, concerning the activating potential of vicarious stimulus presentation. Essentially representative of centralist position, this proposition maintains that peripheral autonomic arousal occurs as a consequence of a central process induced by the instructional set of imagining a fearful situation. Evidence supporti ve of this proposition was provided by Grossberg and Wilson (1968) who found skin conductions (SC) and heart rate (RR) to be elevated in female subjects told to imagine fear invoking situations . An interpretive difficulty was found in that study however in that control subjects, neutral to the content of the scenes, were not physiologically differentiated by the reading of the scene relative to subjects avowing fear to that scene except on the HR measure. A follow-up on the Grossberg and Wilson study (Edelman, 1971) using male subjects did not lend support to the activating potential of vicarious stimulus presentation on physiological processes. That study found that the reading of predetermined fear invoking scenes reliably accelerated heart rate but that when subjects were under the instructional set to imagine the scene, heart rate was at best marginally differentiated from basal level. It is also noteworthy that in both of these aforementioned studies, muscular tension (EMG) typically decreased during the presentation of the vicarious fear stimuli. This latter fact is of importance in that some early theorists had proposed peripheral control of autonomic tension through the skeletal musculature (Jacobson, 1938). The purpose of the present study was to replicate aspects of previous studies relating central arousal and peripheral autonomic processes and to add several procedures which previous research has suggested should be of importance. First of all, subjects were chosen for experimental participation on the basis of their avowed channel of maximal autonomic response. Several investigators have noted stereotypy in autonomic response such that 105
106
ROBERT I. EDELMAN
subjects respond consistently in a particular autonomic end-organ across stressors (Lacey et al., 1951; Lacey and Lacey, 1958). Subjects in the present study were chosen. on the basis of being either heart-rate responders and not GSR responders or GSR responders and not heart-rate responders on the basis of Stern's (1969) Perceived Somatic Reactions to Stress questionnaire. Since there are insufficient validity data relevant to this scale to indicate irs efficiency in predicting autonomic stereotopy, positive results in the present study would tend both to establish the validity of the major proposition at hand while at the same time providing validation data for Stern's scale. A second feature of this experiment was that separate groups of male and female subjects were exposed to the vicarious stimulus presentation. It will be recalled that the Grossberg and Wilson study using female subjects essentially supported the major proposition at hand while the Edelman study using male subjects did not. A final feature of this investigation was that procedural precautions were taken to minimize possible experimenter bias in the presentation of the fear and neutral scenes. This was accomplished by having one experimenter determine the fear and neutral scenes, while a second experimenter simply read the scenes to S in a separate criterion session. The second E was not informed as to which scene was neutral and which was fear-inducing for a given subject. The major hypotheses of the present study may be stated as follows: (1) Subject's verbal report to Stern's scale would reliably predict their channel of maximal autonomic response. (2) The vicarious presentation of arousing material would result in peripheral psychophysiological arousal but only in that channel of maximal autonomic response. (3) Muscular tension would not co-vary with autonomic processes and, since subjects were preselected on the basis of autonomic response and not EMG response, vicarious stimulation would not result in increased muscular tension. (4) Statistically reliable results would be found for female subjects but not for male subjects. METHOD Subjects The subjects were 16 male and eight female students from an introductory psychology class who received extra credit for participation. Ss were chosen from a pool of 187students on the basis of their responses to a modified version of Stern's (1969) Perceived Reactions to Stress questionnaire. In its original form, this questionnaire asks Ss to indicate which of II physiological responses constitute their reaction to personally stressful situations. In the present study, Ss were asked to rank order their response to stress along an intensity dimension and also a frequency dimension using Stern's 11 categories. The purpose of using two separate rank-orderings was to increase the discriminitive power of the instrument and also to avoid the inclusion of Ss who might have responded carelessly or randomly to the group-administered questionnaire. The questionnaire was administered approximately two weeks prior to the actual experimental run. Eight of the 16 male Ss were avowedly high GSR (HGSR) responders but low heart rate (LHR) responders, scoring 0.98 standard deviations (SDs) above the class mean for GSR and 1.03 SDs below the mean for HR reactivity. The remaining eight male Ss avowed the opposite patterning of autonomic responding (LGSR-HHR), scoring 0.90 sn s above the mean for HR and 0.68 sn s below the mean for GSR. The same selection procedure prevailed for females. However, it was not found possible to recruit a sufficient number of Ss for the LGSR-HHR condition who met the
VICARIOUS FEAR INDUCTION AND AVOWED AUTONOMIC STEREOTYPY
107
dual criteria of avowed differential autonomic patterning and willingness to participate in the experiment and this group was accordingly dropped. Scores on the reaction to stress questionnaire for the HGSR-LHR Ss were 0.58 SDs above and 0.85 SDs below the class mean for GSR and HR respectively. Apparatus All physiological variables were monitored on an E & M physiograph. Heart rate was recorded from plate electrodes placed over the wrists and coated with Redux conductive jelly. GSR was recorded using AgjAgCI electrodes coated with redux and placed on the Palmar surface of the second and fourth fingers of the left hand. EMG was recorded from the frontalis muscle according to Lippold's recommendations using AgjAgCI stick-on electrodes coated with Redux. Experimental design and procedure The experimental run for a given subject rook place in two sessions spaced, on the average, a week apart. In the first session, the experimenter explained in detail the purpose of the experiment and what it would entail from the subjects viewpoint. The Fear Survey Schedule (Wolpe and Lang, 1969)was then administered to serve as a vehiclefor determining S's salient fears. After completing the survey, Ss were asked about other fears they might have which were not covered by the survey. The Es were programmed to behave in a friendly manner to encourage self-disclosure, and this first session usually lasted close to an hour. After there was agreement as to S's most important fear both E and S collaborated in writing a 50 word description of that scene devoid of emotionally charged words. The neutral scene was constructed similarly utilizing an item from the survey to which S indicated no anxiety, thereby terminating this first session. A different same-sexed E ran the Ss in the second session. This E was provided with the previously obtained scenes but had no information as to which was the fear and which the neutral scene. S was seated in an overstuffed chair and the appropriate recording electrodes attached. Each scene was then read twice following a counterbalanced ABBA design. The reading of each scene itself consisted of three separate conditions; a 30 sec base period, a 30 sec period at which time the scene was read and finally, a 30 sec period at which time S was given the instructional set to imagine the scene. Each scene presentation was separated by a two minute period to allow physiological measures to stabilize. The experimental design then, was a 2 x 2 x 3 with repeated measures on the last two factors representing respectively the variables Autonomic Stereotypy (HGSR-LHR, LGSR-HHR), Scene Type (fear vs. neutral) and Vicarious Stimulus Presentation (base vs. reading VS. imagining). RESULTS Quantification The quantification procedure followed rules described in a previous study (Edelman, 1971). Data reduction was carried out by a technician unfamiliar with the details or purpose of the study. GSR was converted to micromhos and EMG was converted to millivolts prior to the statistical analyses. Male subjects The GSR and HR data were analyzed according to a type 2 repeated measure & analysis of variance (Winer, 1962, p. 319(. For HR, statistically reliable results were obtained for Scene Type (F-17.30, 4f-l/14, p
108
ROBERT I. EDELMAN
df=2f28, p
/
80
• 78
-----.
"E
a. .a
76
"t:
g
r
74
/'
72 -
70
..
....-
Base
...-- / ./
/'
/'
.--- ---.
/'
.- /._-- ---.
...-
ReOd
Imogine
Cond ition
Fro . 1. Heart rate for male subjects as a function of condition, avowed autonomic response and type of trial.
A similar statistical analysis performed on the GSR data did not attain significance. The EMG data were analyzed by a 2 x 3 repeated measures ANOVA and were not statistically reliable.
Female subjects The EMG, GSR and HR data were analyzed using 2 x 3 repeated measures AN OVA's representing the variables Scene Type and Vicarious Presentation. Statistically reliable results were obtained for Vicarious Presentation (F=4.0, df=2fI4, p<0.05) on the skin conductance measure. Moreover, multiple range tests indicated that skin conductance was reliably higher (p<0.05) during the imagining of the fear scene compared with the neutral scene as can be seen in Fig. 2. DISCUSSION Probably the most salient finding of the present investigation was that imagining a fearful situation elevated autonomic processes more than did a neutral situation. These findings appear consistent with Wolpe's (1969) contention that autonomic processes can
VICARIOUS FEAR INDUCTION AND AVOWED AUTONOMIC STEREOTYPY
109
3·82
l:l
;t
3·80
a>
u
/
c::
.... 0
U
:J
-0 c; 0
/
3·78
/
/
.-------.
/
/
u
c:: :.;;; l/)
3 ·76
/ •
/
/
/
/
. - . Fear tr ial
/ 3 ·74
/
/
. - - . Neutral trial
•
Base
Read
Imagine
Condition
FIG.2. Skin conductance for female subjects avowing high reactivity as a function of condition.
be altered by central states . An important qualification to this statement in the present study, however, is that such arousal is likely to occur in that autonomic channel which is most labiel for a given subject. This finding serves in part to highlight the fact that there is not isomorphic correspondence between autonomic and behavioral measures of anxiety. Under any given set of experimental conditions, these two measures may be correlated or completely uncorrelated-a state of affairs which has led to numerous research strateg ies to enhance the degree of concordance between these measures. Thus, some investigators (Houston, 1971; Thayer, 1971) have attempted to attenuate presumed distorting factors in self-reports, while others (Paul, 1969) including the present investigator have attempted to refine autonomic methodology to achieve greater concordance with behavioral measures. Thus, while the present study does lend credence to Wolpe's position, it is suggested that considerable caution be exercised concerning the general question of defining anxiety as an autonomic response. It is also noteworthy that Stern's scale appeared to have predictive value concerning autonomic arousal. While this finding was not invariant in the present study, it does appear to have heuristic value for autonomic nervous system research which is generally characterized by extremely high inter-subject variability. In the present study, autonomic arousal and muscular tension appeared to occur quite independentl y. This finding is quite consonant with prior research which has generally been inconsistent with the notion that autonomic arousal must be peripherally controlled. REFERENCES R. I. (1971) Desensitization and physiological arousal. J. Person. soc. Psychol. 17, 259-266. R. I. (1970) Verbal report as a prognosticator of physiological arousal to threat. J. abnorm. Psychol. 76, 492-495.
EDELMAN EDELMAN
110
ROBERT I. EDELMAN
HODGES W. F. and SPIELBERGER C. D. (1966) The effects of threat of shock on heart rate for subjects who differ in manifest anxiety and fear of shock. Psychophysiol. 2, 287-294. HOUSTON B. K. (1971) Trait and situational denial and performanceunder stress. J. Person. soc. Psychol. 18, 289-293.
JACOBSON E. (1939) Variation of blood pressure with skeletal tension and relaxation. Ann. Int. Med. 12, 1194-1212.
LACEY J. I. and LACEY BEATRICE C. (1958) Verification and extensionof the principleof autonomic response stereotypy. Am. J. Psychol. 71, 50-73. LACEY J. I. and VAN LEHN R. (1952) Differentialemphasis in somatic response to stress. Psychosom. Med. 23, 185-193.
PAUL G. L. (1969) Physiological effects of relaxation training and hypnotic suggestion. J. abnorm. Psycho/. 74, 425-437.
STERN R. M. and HIGGINS J. D. (1969) Perceived somatic reactions to stress: sex, age and familial occurrence. J. Psychosom. Res. 13, 77-82. THAYER R. E. (1971) Personality and discrepencies between verbal reports and physiological measures of private emotional experiences. J. Personality. 39, 57-69. WINER B. J. (1962) Statistical Principles in Experimental Design. McGraw-Hill, New York. WOLPE J. and LANG P. J. (1969) Fear Survey Schedule Manual. Ed. & Industrial Testing Service. WOLPE J. and LAZARUS A. A. (1966) Behavior Therapy Techniques. Pergamon Press, Oxford.